Method and device for communicating a message on a network and systems using them

ABSTRACT

The communication method concerns communication stations adapted to communicate with each other when a base station supplies a synchronisation signal to mobile stations synchronising on this signal. 
     This method includes a request operation during which a first base station transmits, to a mobile station, a request for the storage in memory and transmission, by the mobile station, of a message, to a message destination communication station which is not synchronised with the first base station.

BACKGROUND OF THE INVENTION

The present invention concerns a method and device for communicating ona network and systems using them. It applies in particular to localwireless networks with centralised architecture, for which eachcommunication is organised between a so-called base communicationstation, also referred to as the “fixed part”, and a mobilecommunication station, also referred to as the “portable part”.

An example of such a communication network is given by the telephonesusing the DECT (Digital Enhanced Cordless Telecommunications) Europeanstandard.

In such a local network, a base station supplies a synchronisationsignal to all the mobile stations present in a cell of the network. Allthe stations (the base station and one or more mobile stations) whichare thus synchronised with each other constitute a cell.

In such a network, there is no communication channel between the cells,nor any synchronisation, and the stations of two different cells cantherefore not communicate with each other.

The document EP 732 817 is known, which describes a procedure forsynchronising adjacent DECT radio cells. This procedure must beperformed regularly (for example every second), which consumes power.This can be a problem for stations powered by a battery.

The document U.S. Pat. No. 5,515,509 is also known, which describes amethod for setting up a communication link between adjacent cells in awireless network. This method uses a control communication channel andequipment which has a relay function. This relay function is permanentand requires dedicated equipment, which is not very flexible, since therelay equipment then loses its mobility.

BRIEF SUMMARY OF THE INVENTION

The present invention sets out to remedy these drawbacks and, inparticular, to make it possible to transmit short messages between twocells situated in the same local area and which are not synchronised.This invention supplies a temporary gateway function which can be usedfor:

notifying a call external to the cell,

notifying the reception of a fax,

notifying the reception of an electronic mail message,

notifying the status of a station and, in particular, a statusconcerning the base station (air interface busy or free, etc).

To this end, the present invention relates, according to a first aspect,to a method of communicating between communication stations adapted tocommunicate with each other when at least one of said communicationstations supplies a synchronisation signal, said station thenfunctioning in “base station” mode and the stations not supplying asynchronisation signal but synchronising on a synchronisation signalsent by a station functioning in base station mode then functioning in“mobile station” mode,

characterized in that it includes a request operation during which afirst base station transmits, to a mobile station, a request for thestorage in memory and transmission, by said mobile station, of amessage, to a communication station for which the message is intendedand which is not synchronised with said first base station.

The present invention relates, according to a second aspect, to a methodof communicating between communication stations adapted to communicatewith each other when at least one of said communication stationssupplies a synchronisation signal, said station then functioning in“base station” mode and the stations not supplying a synchronisationsignal but synchronising on a synchronisation signal sent by a stationfunctioning in base station mode then functioning in “mobile station”mode, characterized in that it includes:

a first operation of receiving a message, during which a mobile stationsynchronised with a first base station receives a message coming fromsaid first base station,

an operation of detachment and attachment, during which said mobilestation synchronises with a second base station, without the two basestations synchronising with each other, and

a second transmission operation, during which said mobile stationtransmits said message to said second base station.

By virtue of these provisions, a communication gateway can beestablished temporarily between two non-synchronised cells. In addition,it is not necessary to regularly synchronise two cells nor to fix thestatus of a communication station as a relay station. Quite thecontrary, the communication link between two non-synchronised cells isset up solely when a message is to be transmitted from one cell to theother. In addition, it is not necessary to have equipment dedicated tothe role of relay in the system in order to be able to communicatebetween two non-synchronised cells. The relay role for a mobile stationis temporary and dynamic, and each mobile station in the system canbecome a relay at a given moment according to its availability.

In addition, implementing the invention is easy and, for the user,transparent.

According to particular characteristics, the method of the invention assuccinctly disclosed above also includes a response operation duringwhich said mobile station transmits to said first base station a messageof acceptance or refusal of transmission of said message to the messagedestination station.

By virtue of these provisions, it is the mobile station which decideswhether or not it agrees to serve as a messenger. These characteristicsenable it to take account of current or future communications in whichit is a party, a service quality to be provided to its user, its energyresources, etc.

According to particular characteristics of the method which is theobject of the present invention as succinctly disclosed above, as apreliminary to said request operation, the first base station performsan operation of selecting, from a so-called “location” table, the mobilestation which is the destination of the request to store in memory andtransmit.

Preferentially, if, during the response operation, the mobile stationtransmits, to the first base station, a message refusing transmission ofsaid message, the base station performs a new operation of selecting,from a so-called “location” table, a mobile station which is thedestination of the request to store in memory and transmit.

By virtue of each of these provisions, the allocation of the role ofstation which conveys the message between the two cells is not fixed inadvance but by a dynamic selection, which makes it possible to takeaccount of the current or future traffic, a service quality to beprovided, available energy resources, etc.

According to particular characteristics of the present invention assuccinctly disclosed above, during the request operation, the first basestation transmits to the mobile station:

the content of the message to be transmitted to the message destinationstation,

an identifier of the message destination station,

an identifier of the first base station, and/or

an identifier of a source station which supplies, to the first basestation, the message to be transmitted to the message destinationstation.

By virtue of all these provisions, a single transmission from the firstbase station suffices for the mobile station which serves as a relay andthe message destination station to be able to receive and transmit themessage and reply to the first base station.

According to particular characteristics of the present invention assuccinctly disclosed above, said message represents a traffic betweenthe mobile stations synchronised on the first base station and the firstbase station.

By virtue of these provisions, the traffic of the cell whose basestation is the first base station can be known from the second basestation and:

the traffic of the two cells can then be balanced by transferring one ormore communications from one base station to the other, or

when the traffic is very low for each base station, the two cells can bemerged, one of the base stations then switching into mobile stationoperating mode and synchronising, along with all the mobile stationswhich were synchronised with it, with the remaining base station.

According to a third aspect, the present invention relates to a devicefor communication between communication stations adapted to communicatewith each other when at least one of said communication stationssupplies a synchronisation signal, said station then functioning in“base station” mode and the stations not supplying a synchronisationsignal but synchronising on a synchronisation signal transmitted by astation functioning in base station mode then functioning in “mobilestation” mode,

characterized in that it has, in a first base station, a request meansadapted to transmit, to a mobile station, a request for the storage inmemory and transmission, by said mobile station, of a message, to amessage destination communication station which is not synchronised withsaid first base station.

According to a fourth aspect, the present invention relates to a devicefor communication between communication stations adapted to communicatewith each other when at least one of said communication stationssupplies a synchronisation signal, said station then functioning in“mobile station” mode and the stations not supplying a synchronisationsignal but synchronising on a synchronisation signal transmitted by astation functioning in base station mode then functioning in “mobilestation” mode, characterized in that it has:

in a mobile station synchronised with a first base station, a firstmeans of receiving a message, adapted to receive a message coming fromsaid base station,

a detachment and attachment means adapted to synchronise said mobilestation with a second base station, without the two base stationssynchronising with each other,

the transmission means also being adapted to transmit said message tosaid second base station when said mobile station is synchronised withsaid second base station.

The invention also relates to a network, a computer, a camera, afacsimile machine, a photographic apparatus, a television receiver, aprinter, a scanner and an audio/video player, characterized in that theyhave a device according to the third and/or fourth aspects of theinvention as succinctly disclosed above.

The invention also relates to:

an information storage means which can be read by a computer or amicroprocessor storing instructions of a computer program characterizedin that it makes it possible to implement the method according to thefirst and/or second aspects of the invention as succinctly disclosedabove, and

an information storage means which is removable, partially or totally,and which can be read by a computer or a microprocessor storinginstructions of a computer program characterized in that it makes itpossible to implement the method according to the first and/or secondaspects of the invention as succinctly disclosed above.

The invention also relates to a computer program product comprisingsoftware code portions for implementing a method according to the firstand/or second aspects of the invention as succinctly disclosed above.

The preferential or particular characteristics, and the advantages ofthis device, of this computer, of this camera, of this facsimilemachine, of this photographic apparatus, of this television receiver, ofthis printer, of this scanner, of this audio/video player, of theseinformation storage means and of this computer program product beingidentical to those of the method according to the first and secondaspects of the invention as succinctly disclosed above, these advantagesare not repeated here.

The present invention also relates, according to a fifth aspect, to amethod of communicating between communication stations adapted tocommunicate with each other when at least one of said communicationstations supplies a synchronisation signal, said station thenfunctioning in “base station” mode, and the stations not supplying asynchronisation signal but synchronising on a synchronisation signaltransmitted by a station functioning in base station mode thenfunctioning in “mobile station” mode, wherein, for at least onecommunication to be effected between a so-called “source” station and aso-called “destination” station which is not synchronised with saidsource station, said source station performs:

an operation of synchronisation with:

a base station with which said destination station is synchronised whenthe destination station is functioning in mobile station mode, or

with the destination station if it is functioning in base station mode,and

an operation of communicating with the destination station.

According to a sixth aspect, the present invention relates to a methodof communicating between communication stations adapted to communicatewith each other when at least one of said communication stationssupplies a synchronisation signal, said station then functioning in“base station” mode, and the stations not supplying a synchronisationsignal but synchronising on a synchronisation signal transmitted by astation functioning in base station mode then functioning in “mobilestation” mode,

wherein, for at least one communication to be effected between aso-called “source” station and a so-called “destination” station, saiddestination station performs:

an operation of receiving a message coming from the source stationfunctioning in mobile station mode,

an operation of synchronising with the source station functioning inbase station mode, and

an operation of communicating with the source station functioning inbase station mode.

Thus, when a source station has a message to transmit to another,destination, station, with which it is not synchronised, it synchronisesfirst of all with a destination station, possibly by means of a basestation with which the destination station is synchronised, and thencommunicates the message in question to the destination station.

By virtue of these provisions, it is not necessary to regularlysynchronise two cells nor to fix the status of a communication stationas a relay station. Quite the contrary, the communication link betweentwo non-synchronised cells is set up solely when a message is to betransmitted from one cell to the other.

In addition, the implementation of the present invention is easy and,for the user, transparent. It enables the destination station to receivea message from a source external to the cell (for example with a view totaking an external call without any configuration on the part of a user.

The implementation of the present invention thus makes it possible toresolve one of the problems of distributed communications: the break inthe communication link with the outside world, that is to say the factthat the stations in a cell cannot receive a message from stationsexternal to this cell.

According to particular characteristics of the method of the inventionas succinctly disclosed above, following the communication operation,the destination station performs a detachment and attachment operationduring which the destination station synchronises with the sourcestation, if the latter is functioning in base station mode, and,otherwise, with a base station with which the source station issynchronised.

By virtue of these provisions, when the source station is connected toan external network, the destination station can enter intocommunication with this external network.

According to a seventh aspect, the present invention relates to a devicefor communicating between communication stations adapted to communicatewith each other when at least one of said communication stationssupplies a synchronisation signal, said station then functioning in“base station” mode, and the stations not supplying a synchronisationsignal but synchronising on a synchronisation signal transmitted by astation functioning in base station mode then functioning in “mobilestation” mode, characterized in that it has, for at least onecommunication to be effected between a so-called “source” station and aso-called “destination” station which is not synchronised with saidsource station, in said source station:

a synchronisation means adapted to synchronise said source station with:

a base station with which said destination station is synchronised ifthe destination station is functioning in mobile station mode, or

the destination station if it is functioning in base station mode, and

a communication means adapted to communicate with the destinationstation.

According to an eighth aspect, the present invention relates to a devicefor communicating between communication stations adapted to communicatewith each other when at least one of said communication stationssupplies a synchronisation signal, said station then functioning in“base station” mode, and the stations not supplying a synchronisationsignal but synchronising on a synchronisation signal transmitted by astation functioning in base station mode then functioning in “mobilestation” mode,

characterized in that it has, for at least one communication to beeffected between a so-called “source” station and a so-called“destination” station, in said destination station:

a means of receiving a message coming from the source stationfunctioning in mobile station mode,

a means of synchronising with the source station functioning in basestation mode, and

a means of communicating with the source station functioning in basestation mode.

The invention also relates to a network, a computer, a camera, afacsimile machine, a photographic apparatus, a television receiver, aprinter, a scanner and an audio/video player, characterized in that theyhave a device according to the seventh and/or eighth aspects of theinvention as succinctly disclosed above.

The invention also relates to:

an information storage means which can be read by a computer or amicroprocessor storing instructions of a computer program characterizedin that it makes it possible to implement the method according to thefifth and/or sixth aspects of the invention as succinctly disclosedabove, and

an information storage means which is removable, partially or totally,and which can be read by a computer or a microprocessor storinginstructions of a computer program characterized in that it makes itpossible to implement the method according to the fifth and/or sixthaspects of the invention as succinctly disclosed above.

The invention also relates to a computer program product comprisingsoftware code portions for implementing a method according to the fifthand/or sixth aspects of the invention as succinctly disclosed above.

The preferential or particular characteristics, and the advantages ofthese devices, of this computer, of this camera, of this facsimilemachine, of this photographic apparatus, of this television receiver, ofthis printer, of this scanner, of this audio/video player, of theseinformation storage means and of this computer program product beingidentical to those of the method according to the fifth and/or sixthaspects of the invention as succinctly disclosed above, these advantagesare not repeated here.

The communication protocol according to the DECT standard enablessubcells to be created, in a temporary fashion, for example during theperiod of a communication requiring a large passband. In this case, whenthe so-called principal cell has created a first communication subcell,that is to say when several stations of the principal cell aresynchronised with each other, and the first subcell has created a secondsubcell, the principal cell has, at the present time, no means ofguaranteeing the delivery of a message to the second subcell.

This is because the principal cell is completely ignorant of theexistence of this second subcell.

The document U.S. Pat. No. 5,802,473 (Nortel) is known, which describesa method for determining, in an automatic process, the current topologyof a cellular system. This method is based on the measurement of areceived signal strength indicator (RSSI) between base stations in orderto supply an initial topology of the system and to determine which cellhas the greatest probability of supporting a link with a portable user(a portable station). The data are based on a static configuration ofthe base stations, which are all synchronised with each other, and aremanaged by a single central system. This method cannot therefore beadapted to distributed communications, to their non-synchronisedcharacteristic and to their dynamic change.

The document U.S. Pat. No. 4,644,532 (IBM) is also known, which concernsa method for keeping up to date a topology data base in a network havingat least one control node. A control node according to this document canbe compared with a base station in accordance with the DECT standard.However, with the method proposed by this document, each time there is achange to the network, a broadcast is made to inform all the nodes inthe system. This procedure unnecessarily takes up radio passband.

The present invention sets out to remedy these drawbacks and, inparticular, to allow the transmission of a message representing thelocation of a particular station.

In particular, the message enables:

a base station to be informed, when necessary, of the reorganisation ofa distributed communication environment;

a base station of a first subcell to inform the base station of theprincipal cell, when necessary, of the existence of a second subcell ofthe first subcell; and/or

a base station of a first subcell to inform the base station of a secondsubcell of the first subcell of the disappearance of the first subcell.

To this end, the present invention relates, according to a ninth aspect,to a method of communicating between communication stations adapted tocommunicate with each other when at least one of said communicationstations supplies a synchronisation signal, said station thenfunctioning in “base station” mode and the stations not supplying asynchronisation signal but synchronising on a synchronisation signalsent by a station functioning in base station mode then functioning in“mobile station” mode, characterized in that a first station of a firstcell performs:

an operation of determining a need for information on a second station,concerning a cell in which at least one so-called “third” station issituated, and

when such information is necessary, an operation of transmitting, to thesecond station, a message representing the cell in which at least onethird station is situated.

The present invention relates, according to a tenth aspect, to a methodof communicating between communication stations adapted to communicatewith each other when at least one of said communication stationssupplies a synchronisation signal, said station then functioning in“base station” mode and the stations not supplying a synchronisationsignal but synchronising on a synchronisation signal sent by a stationfunctioning in base station mode then functioning in “mobile station”mode, characterized in that it includes an operation of updating alocation table during which said first station stores in memory,associated with another station, an identifier for a station with whichsaid other station is synchronised.

By virtue of these provisions, each station, whether it is situated inthe principal cell, in the first cell or in the second cell, can bejoined at any time. In addition, the present invention offers completetransparency for the users of the network, of any reorganisation ofsubcells, and makes it possible to take into account any possible changein the distributed communication system.

Thus the implementation of the present invention minimises the use ofradio resources, with a view to transmitting information concerning thelocation of the stations in the system.

According to a particular characteristic, a third station is merged withthe first station.

By virtue of these provisions, a base station which wishes to switch tomobile station operating mode can inform the mobile stations which aresynchronised with it of this new situation. The mobile stations informedcan thus either resynchronise on another base station, or reform a newcell, switching one of the mobile stations into base station operatingmode. This avoids abruptly cutting the communication link between thesemobile stations.

According to a particular characteristic, during the operation ofdetermining the necessity for information, said first station determinesthat information is necessary when:

it is functioning as a base station;

it receives information intended for a station which is not synchronisedwith it.

By virtue of these provisions, the second station is informed of thelocation of the third station only when it attempts to contact it, whichsaves on radio resources and makes it possible to obtain thisinformation dynamically.

According to a particular characteristic, during said transmissionoperation, the first station transmits, to the second station, a messagerepresenting a base station with which the third station wassynchronised.

By virtue of these provisions, the second station is capable of locatingthe third non-synchronised station, and thus to synchronise with thethird station in order to transfer a message to it. This message can forexample come from a base station connected to a telephone network, whichreceives a call intended for the third station then non-synchronisedwith this base station. By virtue of these provisions, it is thenpossible to correctly locate the third station and to inform it that acall which is intended for it is waiting.

According to a particular characteristic, this communication methodincludes an operation of updating a location table during which saidfirst station stores in memory, associated with a third station, anidentifier for a station with which said third station is synchronised.

By virtue of these provisions, a base station is kept informed of thereorganisation of its subcells, which enables it to correctly route themessages intended for stations belonging to these subcells.

According to a particular characteristic, said first station performssaid updating operation when it receives, from a third station, adetachment message identifying a base station with which the thirdstation will synchronise or indicating that the third station willfunction in base station mode.

According to a particular characteristic, said first station performssaid updating operation when it receives, from another first station, amessage representing a base station with which said third station issynchronised.

By virtue of these provisions, the updating of the location informationis performed dynamically and solely when there is a change in thetopology of the system, such as the disappearance of a subcell.

According to a particular characteristic, during the operation ofdetermining the necessity for information, said first station determinesthat information is necessary when:

the first station is functioning as a base station;

at least one mobile station has been synchronised with said firststation and has synchronised with another base station or has switchedinto base station mode, and

the first station switches into mobile station mode.

By virtue of these provisions, the information concerning the locationof the subcells generated by the first station then functioning in basestation mode can be transferred to another base station when the firststation wishes to switch to mobile station operating mode. This makes itpossible not to lose the access path to the stations constituting thesubcells. The determination of a need for information makes it possibleto adapt to a dynamic and rapid reorganisation of the tree of the cellsof the DECT local network without consuming too much radio passband.

According to a particular characteristic, during said transmissionoperation, said first station transmits, to the third station, a messagerepresenting a base station with which the first station willsynchronise.

By virtue of these provisions, the first station can inform the thirdstation of its future location. Thus, if the third station wishes toremain synchronised with the first station, it can “follow” it.

According to an eleventh aspect, the present invention relates to adevice for communicating between communication stations adapted tocommunicate with each other when at least one of said communicationstations supplies a synchronisation signal, said station thenfunctioning in “base station” mode and the stations not supplying asynchronisation signal but synchronising on a synchronisation signalsent by a station functioning in base station mode then functioning in“mobile station” mode, characterized in that it has:

means for determining the need to inform a second station, concerning acell in which at least one so-called “third” station is situated, and

transmission means for transmitting, when such information is necessary,to the second station, a message representing the cell in which at leastone third station is situated.

According to a twelfth aspect, the present invention relates to a devicefor communicating between communication stations adapted to communicatewith each other when at least one of said communication stationssupplies a synchronisation signal, said station then functioning in“base station” mode and the stations not supplying a synchronisationsignal but synchronising on a synchronisation signal sent by a stationfunctioning in base station mode then functioning in “mobile station”mode, characterized in that it has location table updating means forstoring in memory, associated with another station, an identifier for astation with which said other station is synchronised.

The invention also relates to a network, a computer, a camera, afacsimile machine, a photographic apparatus, a television receiver, aprinter, a scanner and an audio/video player, characterized in that theyhave a device according to the eleventh and/or twelfth aspects of theinvention as succinctly disclosed above.

The invention also relates to:

an information storage means which can be read by a computer or amicroprocessor storing instructions of a computer program characterizedin that it makes it possible to implement the method according to theninth and/or tenth aspects of the invention as succinctly disclosedabove, and

an information storage means which is removable, partially or totally,and which can be read by a computer or a microprocessor storinginstructions of a computer program characterized in that it makes itpossible to implement the method according to the ninth and/or tenthaspects of the invention as succinctly disclosed above.

The invention also relates to a computer program product comprisingsoftware code portions for implementing a method according to the ninthand/or tenth aspects of the invention as succinctly disclosed above.

The preferential or particular characteristics, and the advantages ofthis device, of this computer, of this camera, of this facsimilemachine, of this photographic apparatus, of this television receiver, ofthis printer, of this scanner, of this audio/video player, of theseinformation storage means and of this computer program product beingidentical to those of the method according to the ninth and/or tenthaspects of the invention as succinctly disclosed above, these advantagesare not repeated here.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Other advantages, aims and characteristics of the present invention willemerge from the following description, given with regard to theaccompanying drawings, in which:

FIG. 1 depicts schematically the architecture of an electronic circuitincorporated in a communication device in accordance with the third andfourth aspects of the present invention and adapted to function in basestation mode,

FIG. 2 depicts schematically the architecture of an electronic circuitincorporated in a communication device in accordance with the third andfourth aspects of the present invention and adapted to function inmobile station mode, in connection with the electronic circuit in FIG.1,

FIG. 3 depicts, schematically, a network implementing the presentinvention and including two communication stations functioning in basestation mode and two communication stations functioning in mobilestation mode,

FIGS. 4 a and 4 b depict base station location tables,

FIGS. 5 and 6 depict an algorithm executed by a station functioning inbase station mode for transmitting a request to relay a message to amobile station,

FIG. 7 depicts an algorithm executed by a station functioning in mobilestation mode on reception of a request to relay a message,

FIG. 8 depicts an algorithm executed by a station functioning in mobilestation mode for relaying a message,

FIG. 9 depicts an algorithm executed by a station functioning in mobilestation mode having relayed a message,

FIG. 10 depicts an algorithm executed by a communication station havingreceived a short message,

FIG. 11 depicts a succession of radio messages for the transmission of amessage between two communication stations belonging to twonon-synchronised local cells,

FIG. 12 depicts an algorithm executed by a second base station which hasreceived a message informing it of the load on a first base station,

FIG. 13 depicts an algorithm executed by a first base station which hasreceived a response coming from a second base station to a messageinforming of the load on the first base station,

FIG. 14 depicts schematically the architecture of an electronic circuitincorporated in a source station in accordance with the seventh andeighth aspects of the present invention,

FIG. 15 depicts schematically the architecture of an electronic circuitincorporated in a destination station, in connection with the electroniccircuit illustrated in FIG. 14,

FIG. 16 depicts schematically a network implementing the presentinvention and including two communication stations functioning in basestation mode, one of which is connected to an external network, and acommunication station functioning in mobile station mode,

FIGS. 17 a and 17 b depict base station location tables,

FIGS. 18 and 19 depict an algorithm executed by a source stationfunctioning initially in base station mode, in order to send a messageto a destination station,

FIGS. 20 and 21 depict an algorithm executed by a destination station onreception of a message coming from a source which has implemented thealgorithm illustrated in FIGS. 18 and 19,

FIG. 22 depicts a succession of radio messages for transmitting amessage between two stations implementing respectively the algorithmsillustrated in FIGS. 18 and 19 on the one hand and 20 and 21 on theother hand,

FIG. 23 depicts schematically the architecture of an electronic circuitincorporated in a communication device in accordance with the eleventhand twelfth aspects of the present invention and adapted to function inbase station mode,

FIG. 24 depicts schematically the architecture of an electronic circuitincorporated in a communication device in accordance with the eleventhand twelfth aspects of the present invention and adapted to function inmobile station mode, in connection with the electronic circuit in FIG.23,

FIGS. 25 and 26 depict examples of a network configuration for which thepresent invention offers a particular advantage,

FIG. 27 depicts a succession of message transmissions in accordance withthe present invention, in a first embodiment,

FIG. 28 depicts a succession of message transmissions in accordance withthe present invention, in a second embodiment,

FIG. 29 depicts an algorithm executed by a relay mobile station whichsends a relay message to a communication station which is notsynchronised with the source of said message,

FIG. 30 depicts an algorithm executed by a relay mobile station whichhas received a new location information message,

FIG. 31 depicts an algorithm executed by a relay mobile stationresynchronising with the initial base station, and

FIG. 32 depicts the algorithm executed by a base station which hasreceived a message giving information on a station serving as a relay.

DETAILED DESCRIPTION OF THE INVENTION

Knowing that so-called “hybrid” communication stations can operateeither in base station mode or in mobile station mode, in the remainderof the description the term “base station” will encompass on the onehand the communication stations which can function only according tobase station operating mode and on the other hand the hybridcommunication stations temporarily functioning in base station mode.Likewise, in the remainder of the description, the term “mobile station”will encompass on the one hand the communication stations which canfunction only according to mobile station operating mode and one theother hand the hybrid communication stations functioning temporarily inmobile station mode.

In general terms, it will be said that a station is synchronised with abase station either when it functions in mobile station mode and issynchronised with a base station or when it functions itself in basestation mode.

FIG. 1 depicts the electronic circuit of a wireless communicationdevice, using the DECT European standard (specified by the ETSI, ETS 300175, 1991), which can be connected to a network of the STN (SwitchedTelecommunication Network), Ethernet etc type.

This device can be either a DECT base station, or a DECT hybrid station.A DECT base station is responsible notably for providing thesynchronisation of the system. A hybrid station is a communicationstation which can alternately operate as a base station or as a mobilestation. This communication device can be integrated into equipment ofthe computer, printer, fax etc type or be connected to one of the abovementioned items of equipment. The electronic circuit 100 includes,connected together by an address and data bus 102:

a radio unit 101, provided with an antenna 103,

an input/output controller 107,

a network controller 108,

a central processing unit 106,

a read only memory ROM 105, and

a random access memory RAM 104.

In addition, an electrical power supply 109 is provided for powering allthe components of the electronic circuit 100 (the electrical connectionsconcerning the power supply 109 are not shown).

The network controller 108 manages the interface with an externalnetwork 110, for example of the Switched Telephone Network type.

The input/output controller is connected to an information source (forexample an image, sound, text or graphics sensor, a telephone, afacsimile machine, a photographic apparatus, a video camera, a camcorderetc) and/or to an information destination (for example a televisionreceiver, a monitor, a music system, a telephone, a facsimile machine, avideo recorder etc).

All the components illustrated in FIG. 1 are well known to personsskilled in the art of communication circuits with a processor and moregenerally information processing circuits. They are therefore notdetailed here. The electronic circuit 100 and in particular the centralunit 106 are adapted to exploit all the capabilities of the DECTstandard known up to the time of the present invention.

The central unit 106 is also adapted to implement the method of theinvention and, in particular, the flow diagrams illustrated in thefigures.

The random access memory 104 stores, in registers which, forconvenience, each bear the same name as the data which they contain:

“Location_table”: table containing the data concerning the location ofthe stations in the system;

“ID”: a variable representing the index in the location table of thelast mobile station which took the role of relay station. Oninitialisation of the system, ID takes the value 0 corresponding to themobile station situated on the first row of the location table;

“IM”: a variable representing the current index of the mobile stationrequested to become a relay station;

“NM”: a variable representing the number of mobile stations contained inthe location table;

“CI”: a variable representing the load on the cell (the ratio betweenthe passband used and the available passband);

“CI_received”: a variable representing the load on an adjacent cell,whose value is received from the base station of the adjacent cell (theratio between the passband used and the available passband);

“CM”: a message field; and

“CR”: a response field.

The read only memory 105 stores, in registers which, for convenience,each bear the same name as the data which it contains:

“T1”: the value of the maximum time to wait between the sending of amessage “request_relay” and the reception of a message “relay_accepted”or a message “s_rejected”. For example T1 is equal to 200 ms;

“T2”: the value of the maximum time to wait between the reception of amessage “relay_accepted” and the reception of a message“relay_message_response”. For example T2 is equal to 10 s;

“T3”: the value of the maximum time to wait after the sending of adetachment message and attachment to (that is to say synchronisationwith) a new base station. For example T3 is equal to 1 s;

“T4”: the value of the maximum time to wait after the sending of amessage “relay_message” and the reception of a message“relay_message_response”. For example T4 is equal to 500 ms, and

“T5”: the value of the maximum time to wait after the sending of adetachment message and synchronisation with the initial base station.For example T5 is equal to 5 s.

“CI_LOW”: a constant representing the value below which the passband ofthe cell is considered to be too little used;

“CI_HIGH”: a constant representing the value above which the passband ofthe cell is considered to be excessively used.

The read only memory 105 constitutes a means of storing informationwhich can be read by a computer or a microprocessor, storinginstructions of a computer program characterized in that it makes itpossible to implement the method of the invention. According to avariant, the read only memory 105 is removable, partially or totally,and has, for example, a magnetic tape, a flash memory, diskette or afixed-memory compact disc (CD-ROM).

FIG. 2 depicts the electronic circuit of a wireless communicationdevice, using the DECT European standard (specified by the ETSI, ETS 300175, 1991), functioning in mobile station mode.

This device can be either a DECT mobile station, or a DECT hybridstation. This communication device can be integrated into an item ofequipment of the computer, printer, facsimile machine etc type orconnected to one of the aforesaid items of equipment. The electroniccircuit 200 includes, connected together by an address and data bus 202:

a radio unit 201, provided with an antenna 203,

an input/output controller 207,

a central processing unit 206,

a screen 210,

a keyboard 211,

a read only memory ROM 205, and

a random access memory RAM 204.

In addition, an electrical power supply 209 is provided for supplyingall the components of the electronic circuit 200 (the electricalconnections concerning the power supply 209 are not shown).

The input/output controller 207 is connected to an information source(for example an image, sound, text or graphics sensor, a telephone, afacsimile machine, a photographic apparatus, a video camera, a camcorderetc) and/or to an information destination (for example a televisionreceiver, a monitor, a music system, a telephone, a facsimile machine, avideo recorder etc).

All the components illustrated in FIG. 2 are well known to personsskilled in the art of communication circuits with a processor and moregenerally information processing circuits. They are therefore notdetailed here. The electronic circuit 200 and in particular the centralunit 206 are adapted to exploit all the capabilities of the DECTstandard known up to the time of the present invention.

The central unit 206 is also adapted to implement the method of theinvention and, in particular, the flow diagrams illustrated in thefigures.

The random access memory 204 stores, in registers which, forconvenience, each bear the same name as the data which they contain:

“Relay_response”: a temporary variable containing a message of the type“relay_message_response”;

“CI”: a variable representing the load on the cell (the ratio betweenthe passband used and the available passband);

“CI_received”: a variable representing the load on an adjacent cell,whose value is received from the base station of the adjacent cell (theratio between the passband used and the available passband);

“NE”: a variable representing the available energy level of a stationwhose electrical power supply comes from an accumulator or battery;

“CM”: a message field; and

“CR”: a response field.

The read only memory 205 stores, in registers which, for convenience,each bear the same name as the data which it contains:

“T1”: the value of the maximum time to wait between the sending of amessage “request_relay” and the reception of a message “relay_accepted”or a message “relay_rejected”. For example T1 is equal to 200 ms;

“T2”: the value of the maximum time to wait between the reception of amessage “relay_accepted” and the reception of a message“relay_message_response”. For example T2 is equal to 10 s;

“T3”: the value of the maximum time to wait after the sending of adetachment message and synchronisation with a new base station. Forexample T3 is equal to 1 s;

“T4”: the value of the maximum time to wait after the sending of amessage “relay_message” and the reception of a message“relay_message_response”. For example T4 is equal to 500 ms, and

“T5”: the value of the maximum time to wait after the sending of adetachment message and synchronisation with the initial base station.For example T5 is equal to 5 s.

“CI_LOW”: a constant representing the value below which the passband ofthe cell is considered to be too little used;

“CI_HIGH”: a constant representing the value above which the passband ofthe cell is considered to be excessively used.

“NE_MIN”: a constant representing the value of NE below which a mobilestation must refuse to take the role of relay.

The read only memory 205 constitutes a means of storing informationwhich can be read by a computer or a microprocessor, storinginstructions of a computer program characterized in that it makes itpossible to implement the method of the invention. According to avariant, the read only memory 205 is removable, partially or totally,and includes, for example, a magnetic tape, a flash memory, a disketteor a fixed-memory compact disc (CD-ROM).

FIG. 3 depicts a local wireless communication network 310 comprising:

a DECT base station 300, connected to an STN network 311,

a DECT mobile station 301,

a DECT mobile station 302,

a DECT hybrid station 303, functioning initially in mobile station mode.

On initialisation of this system, the mobile stations 301, 302 and 303are synchronised with the base station 300.

In one embodiment of the present invention, if the mobile stations 302and 303 wish to communicate together, the base station 300 initiates asuitable procedure so that the stations 302 and 303 communicatedirectly, without transmitting data through the base station 300. Tothis end, the base station 300 sends a message to the hybrid station303, requesting it to switch into base station mode, and a message tothe mobile station 302, requesting it to synchronise on the station 303.

By virtue of this procedure, a new radio cell 312 is created, whichmakes it possible to increase the radio passband available in the localwireless network.

The problem is that the stations 302 and 303 are no longer correctlysynchronised with the base station 300. Consequently, whilst thestations 302 and 303 constitute a subcell 312 in the local wirelessnetwork, neither the station 301 nor the base station 300 cancommunicate either with the station 302 or with the station 303.

The present invention makes it possible to resolve this problem.

In particular, the present invention aims to transmit short messages(that is to say those which can be contained in the memory of a mobilestation and, preferentially, whose transmission requires one or tworadio frames), making it possible to transfer a command or an item ofinformation from a first communication device to a second communicationdevice, the first device and the second device being situated in radiocells situated in the same local area, but not being synchronised witheach other, nor with the same station functioning in base station mode.The content of the short message can be either intended for the user ofthe destination station (equivalent to a short message known as SMS,standing for “Short Message System” in the GSM standard, the acronym for“Global System for Mobile communication”), or intended for the centralprocessing unit 206 of the destination station.

The short messages thus transmitted have, for example, the followingfunctions:

notifying the user of a station, 302 or 303, of the arrival of anincoming call coming from the network 311 to which the base station 300is connected (for example: a telephone call),

notifying the user of a station, 302 or 303, of the arrival ofelectronic mail,

notifying the user of a station, 302 or 303, of the arrival of a faxmessage (when the base station 300 is integrated into a fax or connectedto equipment of the fax type),

notifying the stations 302 and/or 303 of the state of the base station300 (for example: the load in terms of radio passband, etc).

When the base station 300 wishes to send a short message to the station302, for example, the base station 300 will execute the algorithmillustrated in FIGS. 5 and 6.

It can be seen that, if the station 300 were functioning in mobilestation mode, it would execute the same algorithms illustrated in FIGS.5 and 6.

First of all, during a test 501, the base station 300 attempts to locatethe station 302 by determining whether the identifier of the station 302is situated in a location table illustrated in FIGS. 4 a and 4 b, whichit stores in its random access memory 104.

This table contains:

at top left, the identifier of the station with which the station whichstores the location table is synchronised, or its own identifier if thisstation functions in base station mode, here the identifier 300,

on a first column on the left, the identifiers of all the stations whichare, at one moment or another, synchronised with this base station 300,here the stations 301, 302 and 303,

in a second column, at the centre, the operating mode of the stationidentified at the head of each row, on the left, and

in a third column, on the right, when the station identified at the headof the row is functioning in mobile station mode, the base station withwhich it is synchronised at the moment when the table is read; when thestation identified at the head of the row is functioning in base stationmode, the base station with which it was synchronised before switchingto base station mode.

Thus, in FIG. 4 a, which represents the location table corresponding toa single cell, the three stations 301, 302 and 303 are functioning inmobile station mode, the mode indicated by the letters “PP”, the acronymfor “portable part”, in the central column and are all synchronised onthe station functioning in base station mode 300, indicated in theright-hand column.

The location table illustrated in FIG. 4 b corresponds to the creationof the subcell 312:

the station 301 functions in mobile station mode synchronised with thestation functioning in base station mode 300,

the station 302 functions in mobile station mode synchronised with thestation functioning in base station mode 303, and

the station 303 functions in base station mode (represented by theletters “FP”, the acronym of the words “fixed part”, in the centralcolumn), the right-hand column then indicating that 303 was previouslysynchronised with 300, and that at the end of the existence of thesubcell 312, 303 will resynchronise with 300.

At each modification of the configuration of the system, the basestation 300 updates a location table. The initial location table of thesystem is depicted in FIG. 4 a. This table indicates that the cell, forwhich the station 300 is the base station, has three stations in mobilemode: 301, 302 and 303.

The table depicted in FIG. 4 b indicates the configuration of the systemafter a direct communication cell has been formed between the station302 and the station 303, as described previously. This table indicatesthat the station 301 is still synchronised with the station 300 andthat, on the other hand, the station 303 has switched into base stationmode and the station 302 is synchronised with the station 303.

When the identifier of the station 302 is present in the location tablestored in the random access memory 104 of the station 300, the result ofthe test 501 is positive. When the result of the test 501 is negative,during an operation 502, a failure message is transmitted to the sourceof the message to be transmitted or to the user of the station 300 andthe implementation of the algorithm is terminated until a new message isto be transmitted by the station 300.

When the result of the test 501 is positive, during a test 503, thecentral unit 106 determines whether the station 302 is in the same cellas the station 300, that is to say whether they are both synchronisedwith the same base station or whether one of them is functioning in basestation mode and the other is synchronised on it.

During the test 503, the central unit 106 determines whether or not theindicator indicated in the right-hand column of the location table, inthe row corresponding to station 302, is the identifier of the station300.

When the result of test 503 is positive, during an operation 504, thestation 300 transmits the message which it has to deliver to the station302 in accordance with the procedures known in the implementation of theDECT standard.

When the result of test 503 is negative, during an operation 517, theindex IM takes the value of the index of the last mobile station whichserved as a relay, incremented by one, modulo the value of NM (whichmeans that if ID+1=NM then IM takes the value 0). Thus, if the systemincludes several mobile stations, it will not always be the same mobilestation which will be requested to become a relay station.

Step 517 is followed by step 505, during which the central unit 106determines whether the mobile station corresponding to the index IM isavailable for becoming a relay station. It should be stated here that astation is considered to be available if it is operating in mobilestation mode (and not in base station mode) and if it is not currentlycommunicating (sending or receiving) a message.

When the result of test 505 is negative, the operation 518 is performed.During the operation 518, the index IM is incremented by 1 modulo MN.Next, during a test 519, the central unit 106 determines whether or notthe value of IM is equal to that of ID+1, modulo NM. If the result oftest 519 is positive, the operation 502 is performed.

If the result of 519 is positive, the operation 505 is reiterated withthe new value of IM.

According to a variant, not depicted here, the rotating selection of arelay mobile station (operation 517, 505, 518, 519), can be replaced bya pseudo-random selection.

When the result of test 505 is positive, during an operation 506, thecentral unit 106 sends to the available mobile station, here the station301, a message “request_relay” of the form <CM, 302, 303, 300>, in whichthe first term, CM, represents the content of the message to betransmitted, the second term, here 302, indicates the final destinationof the message, the third term, here 303, indicates the stationfunctioning in base station mode with which the station 301 will have tosynchronise for the transmission of the message, and the fourth term,here 300, indicates the message source station.

Then, during an operation 507, a clock pulse downcounter is initialisedand started. Such a pulse downcounter is known as a timer. The period T1during which its value is positive is known in advance. When its valuereaches “0”, its operation is automatically stopped. In addition, thevariable ID is then updated with the value of IM, so that, when a futurerelay message is transmitted, the selection of the new relay stationdoes not commence with the station corresponding to the index ID.

Next, during a test 508 (FIG. 6), the central unit 106 determineswhether or not a message “relay_accepted” has been received from thestation 301. When the result of the test 508 is negative, during a test509, the central unit 106 determines whether or not a message“relay_rejected” has been received by the station 301. When the resultof the test 509 is negative, during a test 510, the central unit 106determines whether the period T1 has elapsed, by determining whether ornot the value of the timer of period T1 is nil.

When the result of test 510 is negative, test 508 is reiterated. Whenthe result of test 510 is positive, during a test 511, the central unit106 determines whether or not a mobile station other than the station301 (and more generally, whether or not all the mobile stations alreadyconsidered to be available during the message transmission attempt underconsideration) is available in the cell. When the result of 511 isnegative, operation 502 is performed. When the result of test 511 ispositive, operation 506 is reiterated, taking account of the new mobilestation considered to be available.

When the result of test 509 is positive, test 511 is performed. When theresult of test 508 is positive, during an operation 512, a timer ofduration T2 is initialised and started. Then, during a test 513, thecentral unit 106 determines whether or not a message“relay_message_response” has been received from the station 302. Whenthe result of test 513 is negative, during a test 514, the central unit106 determines whether or not the value of the timer of duration T2 isnil.

When the result of test 514 is negative, test 513 is reiterated. Whenthe result of test 514 is positive, during an operation 515, the absenceof a response is processed. For example, test 511 is performed. When theresult of test 513 is positive, during an operation 516, the responsereceived from the station 302 is processed and, in the event of failureof the processing (for example if the message “relay_message_response”contains information representing failure, see operation 711, FIG. 7),the test 511 is performed. FIG. 7 illustrates the algorithm implementedby the station 301, during the functioning of the station 300illustrated in FIGS. 5 and 6, when the station 301 is the stationconsidered as being available during the operation 505.

The central unit 206 of the station 301 determines, during a test 701,whether or not a message “request_relay” for the station 301 has beenreceived. When the result of test 701 is positive, during a test 702,the central unit 206 of the mobile station 301 determines whether or notthe relay role is accepted.

According to a first example of implementation of this test 702, thecentral unit 206 determines whether a communication would be interferedwith by the detachment and attachment operation and, if during theavailability test 702 it is determined that no communication would beinterfered with by a detachment and attachment operation, the result oftest 702 is positive.

According to a second example, the central unit 206 determines whetheror not the station 301 is participating in a current communication and,if it is participating in a current communication, it is determined thata communication would be interfered with by a detachment and attachmentoperation and the result of test 702 is negative.

According to a third example, the central unit 206 determines whether ornot a quantity of energy available to the station 301 is greater than apredetermined quantity and, if during test 702 it is determined that thequantity of energy is greater than said predetermined quantity, theresult of test 702 is positive. Thus the central unit 206 can, where thepower supply to the mobile station comes from an accumulator or battery,determine whether the current value of the available energy level (NE)is greater than a predefined value (NE_MIN), in order to accept or notthe role of relay.

According to a fourth example, if the central unit 206 determines thatthe station 301 will have no message to send or receive during apredetermined period T2 to come, it considers that the role of relaymust be accepted (result of test 702 positive) and that otherwise itmust be refused.

When the result of test 702 is negative, that is to say when the role ofrelay is refused, the central unit 206 causes to be sent to the station301 a message “relay_rejected” of the form <CM, 303, 302, 300> in whichthe first term, CM, represents the content of the message, the secondterm, 303, represents the base station with which the station 301 was tosynchronise, the third term, 302, represents the message destinationstation and the fourth term, 300, represents the station at the sourceof the message.

When the result of the test 702 is positive, that is to say when thestation 301 accepts the role of relay, the central unit 206 causes to besent to the station 301 a message “relay_accepted” of the form <CM, 303,302, 300> in which the first term, CM, represents the content of themessage, the second term, 303, represents the base station with whichthe station 301 is to synchronise, the third term, 302, represents themessage destination station and the fourth term, 300, represents thesource of the message.

Then, during an operation 705, the central unit 206 causes thedetachment of the station 301 from the base station 300, in accordancewith known procedures, including notably the sending of a detachmentmessage to the base station 300.

Then, during an operation 706, the central unit 206 initialises a timerof predetermined duration T3 and starts it. Next, during an operation707, the central unit 206 seeks the base station 303 in order tosynchronise with it. Then, during a test 708, the central unit 206determines whether or not the base station 301 has succeeded insynchronising with the base station 303. When the result of test 708 isnegative, during a test 709, the central unit 206 determines whether ornot the value of the timer of predetermined period T3 is nil. When theresult of test 709 is negative, operation 707 is reiterated. When theresult of test 709 is positive, the central unit 206, which has remainedsynchronised with the base station 300, sends it an attachment messageduring an operation 710.

It should be noted here that one reason why the mobile station 301cannot synchronise with the station 303 may be that the stations 301 and303 are situated at two ends of the local area and that thesynchronisation signal sent by the base station 303 is too weak or toonoisy to be correctly received and used by the mobile station 301.

Then, during an operation 711, the central unit 206 causes the sendingby the station 301 of a message “relay_message_response” of the form<FAILURE, 303, 302, 300> in which the first term “FAILURE” indicatesthat the message to be relayed has not been able to be transferred, thesecond term, 303, represents the base station with which the station 301was to synchronise, the third term 302, represents the messagedestination station and the fourth term, 300, represents the station atthe source of the message.

When the result of test 708 is positive, during an operation 712 (FIG.8), the central unit 206 causes the sending of attachment message to thebase station 303. Then, during an operation 713, the central unit 206causes the sending, to the station 302, of a message “relay_message” ofthe form <CM, 300> in which the first term, CM, represents the contentof the message and the second term, 300, represents the source of themessage.

Next, during an operation 714, the central unit 206 initialises a timerof predetermined duration T4 and starts it. Next, during a test 715, thecentral unit 206 determines whether or not a message“relay_message_response” has been received from the mobile station 302.When the result of test 715 is negative, during a test 716, the centralunit 206 determines whether or not the value of the timer of duration T4is nil. When the result of test 716 is negative, the test 715 isreiterated. When the result of test 716 is positive, during an operation717, a message “response_relay” is formed in the form <NONE, 300, 302>in which the first term indicates that no response has been receivedfrom the station 302, the second term indicates the destination stationfor the message “response_relay” and the third term indicates thestation from which a message “relay_message_response” was awaited.

When the result of test 715 is positive, during an operation 718, amessage “response_relay” is formed in the form <CR, 300, 302> in whichthe first term contains the content of the response, a content drawnfrom the message “relay_message_response”transmitted by the station 302,the second term indicates the destination station for the message“response_relay” and the third term indicates the station from which amessage “relay_message_response” was awaited.

Following one or other of operations 717 and 718, during an operation719 (FIG. 9), the central unit 206 causes the sending, to the basestation 303, of a detachment message. Then, during an operation 720, thecentral unit 206 initialises a timer of predetermined duration T5 andstarts it. Then, during an operation 721, the central unit 206 seeks thebase station 300, the station which is the source of the message“request_relay”.

During a test 722, the central unit 206 determines whether or not thestation 301 has succeeded in synchronising with the base station 300.When the result of test 722 is negative, during a test 723, the centralunit 206 determines whether or not the value of the timer of duration T5is nil. When the result of test 723 is negative, operation 721 isreiterated. When the result of test 723 is positive, the central unit206, which has remained synchronised with the base station 303, sends anattachment message to it, during an operation 724.

When the result of test 722 is positive, during an operation 725, thecentral unit 206 causes an attachment message to be sent by the mobilestation 301 to the base station 300. Then, during an operation 726, thecentral unit 206 causes the message “response_relay” to be sent by themobile station 301 to the station which is the destination of themessage “response_relay” (station 300).

At the end of one of the operations 724 or 726, the implementation ofthe algorithm followed by the central unit of the mobile station 301 isended.

FIG. 10 illustrates an algorithm followed by the central unit 206 of thestation 302 which is the destination of a message coming from thestation 300, by means of the station 301 which served as a relay betweentwo adjacent cells.

First of all, during a test 801, the central unit 206 determines whetheror not a message “relaymessage” has been received. When the result oftest 801 is positive, during an operation 802, the central unit 206performs a processing of the content of the message received. Then,during an operation 803, the central unit 206 effects a sending of amessage “relay_message_response” of the form <CR, 300, 302> in which thefirst term contains the content of the response intended for the station300, indicated by the second term, the third term indicating the stationwhich is the source of this message.

By way of example, the content of this message may mean that the station302 will detach itself from the station 303 and synchronise with thestation 300 with a view to receiving a message.

In FIG. 11, there can be seen, for the four stations 300, 301, 302 and303, depicted by vertical continuous lines, the transmissions andreceptions of messages in the cell including these four stations.

The lapse of time is depicted from top to bottom, each period of a timerbeing depicted by a segment of a vertical straight line.

Only the messages sent when the transmission of a message from station300 to station 302, by means of the stations 301, as a relay station,and 303, as a base station, with the return of a response, is a success,are shown, as well as the periods of searching for synchronisationsignals by the station 301.

First of all, a message “request_relay” 901 is sent by the station 300to the station 301 (operations 506, FIGS. 5 and 701, FIG. 7).

Then a message “relay_accepted” 902 is sent by the station 301 to thestation 300 (operations 704, FIGS. 7 and 508, FIG. 6).

Next a detachment message 903 is sent by the station 301 to the basestation with which it was, until then, synchronised (operation 705).

Then the station 301 seeks the synchronisation signal sent by the basestation 303 (operation 707, FIGS. 7 and 904, FIG. 11).

Next the station 301 sends, to the station 303, an attachment message905 (operation 712, FIG. 8).

Then the station 301 sends, by means of the station 303, to the station302, a message “relay_message” 906 (operations 713, FIG. 8, and 801,FIG. 10).

Next the station 302 sends, by means of the station 303, to the station301, a message “relay_messag_response” 907 (operations 715, FIG. 8 and803, FIG. 10).

Then the station 301 sends a detachment message 908 to the base station303 (operation 719, FIG. 9).

Then the station 301 seeks the synchronisation signal sent by the basestation 300 (operation 721, FIG. 9, and 909, FIG. 11).

Next the station 301 sends an attachment message 910 to the station 300(operation 725, FIG. 9).

Finally, the station 301 sends a message “relay_message_response” 911 tothe station 300 (operations 513, FIG. 6, and 726, FIG. 9).

An example of an application of this invention concerns the distributionof the data stream between two adjacent cells. For this purpose a shortmessage of the type CM=“LOAD_INFO {Identity FP, cell load}” can beexchanged between the two base stations of two adjacent cells, the firstterm representing the identity of the base station of a cell, and thesecond term representing the load on the cell (the ratio between thepassband used and the available passband).

FIG. 12 depicts the algorithm executed by the base station 303 when itreceives a message of the type “LOAD_INFO”, test 1001 positive.

It can be seen here that such a message can be sent by a base station toan adjacent cell when the value of its load CI, permanently stored inrandom access memory 104, is less than the value CI_LOW stored in readonly memory 105.

On receipt of this message, the station 303 prepares and sends aresponse to this message, which contains the control field “LOAD_INFO”as well as the value CI read in the random access memory 204,representing the load on the cell for which the station 303 is the basestation, during an operation 1002. The content of the response, that isto say the content of the field CR, is transmitted as indicated at step803. The station 303 then analyses whether or not its passband isexcessively used, during a test 1003, by determining whether or not thevalue of CI read in the random access memory 204 is greater than thevalue CI_HIGH stored in read only memory 205.

If the result of the test 1003 is positive, during a test 1004, thecentral unit 206 determines whether or not the passband available in thecell for which the station 300 is the base station is too little used.If the result of the test 1004 is negative then no specific processingis to be carried out and the implementation of the algorithm illustratedin FIG. 12 ends. On the other hand, if the result of the test 1004 ispositive, the base station 303 attempts to redirect a communicationestablished in its cell to the base station 300 so that all the stationsto which said communication relates synchronise on the base station 300with a view to balancing the available passband between the two cells.

This can be done only in the case of an internal communication, or inthe case of a communication to an external network or to a printer ifthe base stations 300 and 303 can offer the same service concerning thisexternal communication or this printer.

In order to reroute a communication from the cell of the base station303 to the base station 300, during an operation 1005, the base station303 sends, to the mobile stations involved in the communication to bererouted, a message indicating to them that they should synchronise withthe station 300.

If the result of the test 1003 is negative, during a test 1006, thecentral unit 206 determines whether or not the sum of CI_received andthe value of CI stored in the random access memory 204 is less than thevalue CI_LOW stored in the read only memory 205. When the result of thetest 1006 is positive, the station 303 switches into mobile stationmode, during an operation 1007. In this way, the two cells merge, thatis to say all the mobile stations in the cell for which the base stationwas the station 303 and this station 303 synchronise with the basestation 300.

When the result of test 1006 is negative, no change to the functioningof the station 3003 is made.

FIG. 13 depicts the algorithm executed by the base station 300, when itreceives a response to a short message of the type “LOAD_INFO”. Thereception of this response is determined by a test for the reception ofsuch a message 1101.

During a test 1102, the central unit 106 of the station 300 determineswhether or not the passband of the cell of the base station 300 isexcessively used, determining whether or not the value of the variableCI stored in the random access memory 104 is greater than the value ofCI_HIGH stored in the read only memory 105.

When the result of the test 1102 is positive, during a test 1103, thecentral unit 106 determines whether or not the value of the passband ofthe cell for which the base station is the station 303, a value which istransmitted in the response message, is less than the value CI_LOWstored in the read only memory 105.

When the result of the test 1102 is negative or when the result of thetest 1103 is negative, no change to the functioning of the cell forwhich the station 300 is the base station is made at the initiative ofthe station 300.

When the result of the test 1103 is positive, during an operation 1104,the base station 300 attempts to redirect a communication established inits cell to the base station 303 so that all the stations to which saidcommunication relates synchronise on the base station 303 with a view tobalancing the passband available between the two cells.

This can take place only in the case of an internal communication, or inthe case of a communication to an external network or to a printer ifthe base stations 300 and 303 can offer the same service concerning thisexternal communication or this printer.

In order to reroute a communication from the cell of the base station300 to the base station 303, the base station 300 sends, to the mobilestations involved in the communication to be rerouted, a messageindicating to them that they should synchronise with the station 303.

FIG. 14 depicts the electronic circuit of a wireless communicationdevice, using the DECT European standard (specified by the ETSI, ETS 300175, 1991), which can be connected to a network of the STN (SwitchedTelecommunication Network), Ethernet etc type.

This device can be either a DECT base station, or a DECT hybrid station.A DECT base station is responsible notably for providing thesynchronisation of the system. A hybrid station is a communicationstation which can alternately operate as a base station or as a mobilestation. This communication device can be integrated into equipment ofthe computer, printer, fax etc type or be connected to one of theaforementioned items of equipment. The electronic circuit 1400 includes,connected together by an address and data bus 1402:

a radio unit 1401, provided with an antenna 1403,

an input/output controller 1407,

a network controller 1408,

a central processing unit 1406,

a read only memory ROM 1405, and

a random access memory RAM 1404.

In addition, an electrical power supply 1409 is provided for poweringall the components of the electronic circuit 1400 (the electricalconnections concerning the power supply 1409 are not shown).

The network controller 1408 manages the interface with an externalnetwork 1410, for example of the Switched Telephone Network type.

The input/output controller 1407 is connected to an information source(for example an image, sound, text or graphics sensor, a telephone, afacsimile machine, a photographic apparatus, a video camera, a camcorderetc) and/or to an information destination (for example a televisionreceiver, a monitor, a music system, a telephone, a facsimile machine, avideo recorder etc).

All the components illustrated in FIG. 14 are well known to personsskilled in the art of communication circuits with a processor and moregenerally information processing circuits. They are therefore notdetailed here. The electronic circuit 1400 and in particular the centralunit 1406 are adapted to exploit all the capabilities of the DECTstandard known up to the time of the present invention.

The central unit 1406 is also adapted to implement the method of theinvention and, in particular, the flow diagrams illustrated in FIGS. 18and 19.

The random access memory 1404 stores, in registers which, forconvenience, each bear the same name as the data which they contain:

“Location_table”: table containing the data concerning the location ofthe stations in the system;

“Base_parameters_table”: table containing the values of the parametersfor operating in base station mode;

“External_message_table”: table of messages coming from the network1410;

“CM”: message field in which there is placed the content of a messageintended for a destination station; and

“CR”: response field in which there is placed a response coming from thedestination of a message.

The read only memory 1405 stores, in registers which, for convenience,each bear the same name as the data which they contain:

“T6”: the value of the maximum period allowed for a station tosynchronise with a base station (see tests 1911 and 1912, FIG. 19). Forexample T6 is equal to 1 second;

“T7”: value of the maximum period allowed for receiving a responsemessage after having transmitted an information message (see tests 1915and 1916, FIG. 19). For example, T7 is equal to 500 ms; and

“T8”: the value of the maximum period allowed for the destinationstation to synchronise with a station which has transmitted aninformation message to it (see operation 1919, FIG. 19). For example T8is equal to 5 s.

The read only memory 1405 constitutes a means of storing informationwhich can be read by a computer or a microprocessor, storinginstructions of a computer program characterized in that it makes itpossible to implement the method of the invention. According to avariant, the read only memory 1405 is removable, partially or totally,and has, for example, a magnetic tape, a flash memory, a diskette or afixed-memory compact disc (CD-ROM).

FIG. 15 depicts the electronic circuit of a wireless communicationdevice, using the DECT European standard (specified by the ETSI, ETS 300175, 1991), functioning in mobile station mode.

This device can be either a DECT mobile station, or a DECT hybridstation. This communication device can be integrated into an item ofequipment of the computer, printer, facsimile machine etc type orconnected to one of the aforesaid items of equipment. The electroniccircuit 1500 includes, connected together by an address and data bus1502:

a radio unit 1501, provided with an antenna 1503,

an input/output controller 1507,

a central processing unit 1506,

a screen 1510,

a keyboard 1511,

a read only memory ROM 1505, and

a random access memory RAM 1504.

In addition, an electrical power supply 1509 is provided for supplyingall the components of the electronic circuit 1500 (the electricalconnections concerning the power supply 1509 are not shown).

The input/output controller 1507 is connected to an information source(for example an image, sound, text or graphics sensor, a telephone, afacsimile machine, a photographic apparatus, a video camera, a camcorderetc) and/or to an information destination (for example a televisionreceiver, a monitor, a music system, a telephone, a facsimile machine, avideo recorder etc).

All the components illustrated in FIG. 15 are well known to personsskilled in the art of communication circuits with a processor and moregenerally information processing circuits. They are therefore notdetailed here. The electronic circuit 1500 and in particular the centralunit 1506 are adapted to exploit all the capabilities of the DECTstandard known up to the time of the present invention.

The central unit 1506 is also adapted to implement the method of theinvention and, in particular, the flow diagrams illustrated in FIGS. 20and 21.

The random access memory 1504 stores, in registers which, forconvenience, each bear the same name as the data which they contain:

“Oper_parameters_table”: table containing the operating parameters ofthe station, such as its operating mode (mobile station or basestation), the identity of the base station with which it issynchronised, etc. This information makes it possible to preserve theoperating state of the station before switching to a different operatingmode, in order to be able to return to the previous operating mode,

“CM”: message field in which there is placed the content of a messagereceived from a source station; and

“CR”: response field in which there is placed a response to betransmitted, in return, to a station which is the source of a receivedmessage.

The read only memory 1505 stores, in registers which, for convenience,each bear the same name as the data which they contain:

“T9”: the value of the maximum period allowed for a station which is thedestination of an information message to synchronise with the sourcestation which has become the base station once again (see tests 2111 and2113, FIG. 21). For example T9 is equal to 1 s.

The read only memory 1505 constitutes a means of storing informationwhich can be read by a computer or a microprocessor, storinginstructions of a computer program characterized in that it makes itpossible to implement the method of the invention. According to avariant, the read only memory 1505 is removable, partially or totally,and includes, for example, a magnetic tape, a flash memory, a disketteor a fixed-memory compact disc (CD-ROM).

FIG. 16 depicts a local wireless communication network 1610 comprising:

a DECT base station 1601, connected to an STM network 1602, in a firstsubcell 1605, and

two DECT stations 1603 and 1604 in a second subcell 1606.

On initialisation of this system, all the mobile stations illustrated inFIG. 16 are synchronised with the base station 1601.

In one embodiment of the present invention, if the mobile stations 1603and 1604 wish to communicate together, the base station 1601 initiates asuitable procedure so that the stations 1603 and 1604 communicatedirectly, without transmitting data through the base station 1601. Tothis end, the base station 1601 sends a message to the hybrid station1603, requesting it to switch into base station mode, and a message tothe mobile station 1604, requesting it to synchronise on the basestation 1603.

By virtue of this procedure, a new radio cell 1606 is created, whichmakes it possible to increase the radio passband available in the localwireless network.

The problem is that the stations 1603 and 1604 are no longer correctlysynchronised with the base station 1601. Consequently, whilst thestations 1603 and 1604 constitute a subcell 1606 in the local wirelessnetwork, the station 1601 cannot communicate either with the station1604 or with the station 1603.

The present invention allows to resolve this problem.

In particular, the present invention aims to transmit short messages(that is to say those which can be contained in the memory of a mobilestation and, preferentially, whose transmission requires one or tworadio frames), making it possible to transfer a command or an item ofinformation from a first communication device to a second communicationdevice, the first device and the second device being situated in radiocells situated in the same local area, but not being synchronised witheach other, nor with the same station functioning in base station mode.The content of the short message can be either intended for the user ofthe destination station (equivalent to a short message known as SMS,standing for “short message system” in the GSM standard, the acronym for“Global System for Mobile communication”, or intended for the centralprocessing unit 1506 of the destination station.

The short messages thus transmitted have, for example, the followingfunctions:

notifying the user of the station 1603 or 1604 of the arrival of anincoming call coming from the network to which the base station 1601 isconnected (for example: a telephone call),

notifying the user of the station 1603 or 1604 of the arrival ofelectronic mail,

notifying the user of the station 1603 or 1604 of the arrival of a faxmessage (when the base station 1601 is integrated into a fax orconnected to equipment of the fax type),

notifying the stations 1603 and/or 1604 of the state of the base station1601 (for example, notification solely of a free air interface). This isbecause it is the base station which switches in order to transmit themessage. Thus, in this case the notification of a busy air interfacemight result in a rejection at step 1807 (communication underway in thecell). Only an indication of availability of the base (free airinterface) seems possible, since thus there is a risk neither of cuttingoff a communication under way nor risk of rejection.

In FIG. 18 it can be seen that, during an operation 1801, the basestation 1601 receives a message coming from the external network 1602and intended for a so-called “destination” station 1604. Then, during anoperation 1802, the base station 1601 seeks the location of thedestination station 1604 by reading a location table stored in therandom access memory 1404 (see FIGS. 17 a and 17 b).

This table contains:

at top left, the identifier of the station with which the station whichstores the location table is synchronised, or its own identifier if thisstation functions in base station mode, here the identifier 1601,

on a first column on the left, the identifiers of all the stations whichare, at one moment or another, synchronised with this base station 1601,here the stations 1604 and 1603,

in a second column, at the centre, the operating mode of the stationidentified at the head of each row, on the left, and

in a third column, on the right, when the station identified at the headof the row is functioning in mobile station mode, the base station withwhich it is synchronised at the moment when the table is read; when thestation identified at the head of the row is functioning in base stationmode, the base station with which it was synchronised before switchingto base station mode.

Thus, in FIG. 17 a, which depicts the location table corresponding to asingle cell, the two stations 1604 and 1603 are functioning in mobilestation mode, the mode indicated by the letters “PP”, the acronym of thewords “portable part”, in the central column and are all synchronised onthe station functioning in base station mode 1601, indicated in theright-hand column.

The location table illustrated in FIG. 17 b corresponds to the creationof the subcell 1606:

the station 1604 functions in mobile station mode synchronised with thestation functioning in base station mode 1603, and

the station 1603 functions in base station mode (represented by theletters “FP”, the acronym of the words “fixed part”, in the centralcolumn), the right-hand column then indicating that 1603 was previouslysynchronised with 1601, and that at the end of the existence of thesubcell 1606, 1603 will attempt to resynchronise with the base station1601.

On each modification of the configuration of the system, the basestation 1601 updates its location table.

During a test 1803, the central unit 1406 determines whether or not thestation 1604 is in the location table. When the result of test 1803 isnegative, during an operation 1805, the call coming from the externalnetwork 1602 is rejected. When the result of test 1803 is positive,during a test 1804, the central unit 1406 determines whether or not thestation 1604 is situated in the cell 1605, by determining whether ornot, in the location table, in the row of the station 1604, theidentifier of the base station 1601 is situated in the right-handcolumn.

When the result of the test 1804 is positive, during an operation 1806,the message intended for the station 1604 is transmitted to it withinthe cell 1605, according to known procedures in accordance with the DECTstandard.

When the result of the test 1804 is negative, during a test 1807, thecentral unit 1406 determines whether or not there is a communicationunder way in the cell 1605. When the result of the test 1807 ispositive, the call rejection operation 1805 is performed.

According to a variant, not shown, when the result of the test 1807 ispositive, the central unit 1406 seeks, in the cell 1605, a stationcapable of functioning in base station mode and of ensuring thecommunications under way, and sends to it a request to change to basestation mode. According to this variant, the station 1601 starts tofunction in mobile station mode if another station takes the role ofbase station, and then performs the operation 1808 (below).

When the result of the test 1807 is negative, during an operation 1808,the processing unit 1406 updates the variables “Base_parameters_table”and “External_message_table” stored in the random access memory 1404.The variable “Base_parameters_tab/e”contains all the informationrepresenting the state of the station 1601 before it switches to mobilestation mode. Notably, “Base_parameters_table” stores all the databasesrelated to the subscription parameters of the mobile stations which areregistered with the base station 1601. The variable“External_message_table” contains all the information necessary to thestation 1601 for it to be able to manage this call when it returns tobase station mode. Notably, this table will make it possible to storewhether there is a call waiting, the number of the person called and ofthe caller, etc.

Then, during an operation 1809, the station 1601 switches into mobilestation operation mode.

Then, during an operation 1910 (FIG. 19), a clock pulse downcounter isinitialised to a positive integer value and activated. Such a pulsedowncounter is known as a “timer”. Its value decreases by one, with eachpulse of a clock or clock divider. The time T6 during which its value ispositive is known in advance. When its value reaches “0”, its operationis automatically stopped.

Next, during a test 1911, the central unit 1406 determines whether ornot the station 1601 has synchronised with the base station 1603. Whenthe result of the test 1911 is negative, during a test 1912, the centralunit 1406 determines whether or not the value of the timer of durationT6 is nil.

When the result of the test 1912 is negative, the test 1911 isreiterated. When the result of the test 1912 is positive, during anoperation 1917, station 1601 switches into base station mode and then,during an operation 1918, restores its base station mode operatingparameters, as they were before the operation 1808, and sends, to theexternal network station which is at the origin of the call of thestation 1604, a message representing failure to make immediatecommunication with the station 1604. Next, the operation 1805 isperformed.

When the result of the test 1911 is positive, during an operation 1913,a message “MESSAGE_INFO” is transmitted to the mobile station 1604, withthe field CM representing an external call, in accordance with theprocedures known in the DECT standard. Then, during an operation 1914, atimer of duration T7 is initialised and started. Next, during a test1915, the central unit 1406 determines whether or not a message“MESSAGE_REP” has been received coming from the mobile station 1604,with a field CR representing an acceptance of a call. When the result ofthe test 1915 is negative, during a test 1916, the central unit 1406determines whether or not the value of the timer of duration T7 is nil.

When the result of the test 1916 is negative, the test 1915 isreiterated. When the result of the test 1916 is positive, the operation1917 is performed. When the result of the test 1915 is positive, duringa test 1920, the central unit 1406 determines whether or not the contentof the response message represents an acceptance. When the result of thetest 1920 is negative, the operation 1917 is performed. When the resultof test 1920 is positive, during an operation 1919, a timer ofpredetermined duration T8 is initialised and activated. During the sameoperation 1919, the station 1601 returns to base station operating modewith the operating parameters stored in the random access memory 1404.

During the operation 1919, if the station 1604 does not synchronise withthe base station 1601 during the duration of the timer, T8, theinterlocutor at the origin of the message intended for the station 1604,on the network 1602, receives, from the station 1601, a messagerepresenting failure of the procedure to get into immediatecommunication with the station 1604.

For a non-urgent message, the timer is not activated during theoperation 1919 since no response is awaited by the correspondent callingby means of the external network. This case applies in particular tonotifications of reception of electronic messages (email) or faxes.

FIGS. 20 and 21 represent an algorithm executed by the station 1604 onreception of a message coming from the station 1601 using the algorithmillustrated in FIGS. 18 and 19. It should be noted here that the station1603 uses the same algorithm when it is the called station.

During a test 2000, the central unit 1506 of the station 1604 determineswhether or not a message of the “MESSAGE_INFO” type has been received.When the result of the test 2000 is negative, the processing of themessage received is in accordance with the specifications of the DECTstandard, during an operation 2001.

When the result of the test 2000 is positive, during a test 2002, thecentral unit 1506 determines whether or not the destination address ofthe message “MESSAGE_INFO” is the address of the station 1604. When theresult of the test 2002 is negative, the operation 2001 is performed.When the result of the test 2002 is positive, during an operation 2003,the central unit 1506 sends a message “MESSAGE_REP” with the field CRrepresenting an acceptance, to the station 1601. This acceptance meanssimply that the station 1604 has correctly received the message comingfrom the station 1601. The acceptance message is returned before theprocessing of the content of the message received, in order to enablethe station 1601, as soon as possible, to return to base station mode.

Then, during an operation 2004, the central unit 1506 reads the messageacceptance request including a content CM, a request which is containedin the message “MESSAGE_INFO”. This is because, in the embodimentdescribed and depicted, the message coming from the external network isa message whose content cannot be inserted in the message“MESSAGE_INFO”, because of its size, and whose communication requires apassband such that it is necessary for a new cell to be created withsolely the stations 1601 (operating in base station mode) and 1604(operating in mobile station mode).

When the content of the message CM represents the arrival of a messagein the form of electronic mail, the message is not accepted as an urgentmessage. In such a case, the terminal receiving the message signifiessolely the correct reception of the message and is therefore not obligedto implement the succession of steps described in FIGS. 20 and 21.

Then, during a test 2005, the central unit 1506 determines whether ornot the content message CM is accepted as an urgent message.

When the result of the test 2005 is negative, the operation 2001 isperformed. When the result of the test 2005 is positive, during anoperation 2016, the operating mode of the station 1604 is stored inrandom access memory 1504 and, in particular, the operating mode, basestation or mobile station and, optionally, the identifier of the basestation with which the station 1604 is synchronised.

Then, during a test 2107 (FIG. 21), the central unit 1506 determineswhether or not the operating mode is that of base station. When theresult is positive, during an operation 2108:

if no mobile station is synchronised with the base station 1604, thestation 1604 switches into mobile station operating mode;

if at least one mobile station is synchronised with the base station1604, the base station 1604 sends a request to change base station toone or all of the mobile stations in the cell 1606 (operation not shownin FIG. 21);

in all cases, the base station 1604 then switches into mobile stationmode.

When the result of test 2107 is negative, during an operation 2106, thecentral unit 1506 causes to be sent, by the station 1604, a detachmentmessage to the base station of the cell 1606, indicating to it that itis leaving the cell.

Following one of the operations 2106 or 2108, during an operation 2109,the central unit 1506 attempts to synchronise with the station whichsent the message “MESSAGE_INFO” (the latter then functioning in basestation mode).

Next, during an operation 2110, the central unit 1506 initialises atimer of predetermined duration T9 and activates it. Then, during a test2111, the central unit 1506 determines whether or not thesynchronisation with the station 1601 has been effected. When the resultof the test 2111 is negative, during a test 2113, the central unit 1506determines whether or not the value of the timer of duration T9 is nil.When the result of the test 2113 is negative, the test 2111 isreiterated. When the result of the test 2113 is positive, during anoperation 2114, a synchronisation failure procedure is effected and theinitial operating state of the station 1604, with its operatingparameters stored in the random access memory 1504, is restored. In theevent of failure of synchronisation with the base station with which thestation 1604 was, if applicable, initially synchronised, or in the eventof the presence of a new base station, the station 1604 synchroniseswith any base station present.

When the result of test 2111 is positive, during an operation 2112, thecentral unit 1506 causes the attachment of the station 1604 with thestation 1601. Next, the cell which includes solely the stations 1601 and1604 is created and communication is established.

In FIG. 22, there can be seen, for the three stations 1601, 1603 and1604, shown in vertical continuous lines, the transmissions andreceptions of messages.

The elapse of time is depicted from top to bottom, each duration of atimer being depicted by a segment of a vertical straight line.

Only the messages sent when a message is transmitted from the station1601 to the station 1604 is a success and when the station 1604 attachesto the station 1601 are shown, along with certain operations performedby the stations 1601 and 1604.

Following the switching of the station 1601 into mobile station mode,operation 401 (operation 1809, FIG. 18), the station 1601 performs anoperation of synchronisation with the station 1603, during an operation402 (operation 1911, FIG. 19). Then the station 1601 sends, by means ofthe base station 1603, a message “MESSAGE_INFO <CM, 1604, 1601>”, inwhich the first term includes the content of the message, the secondidentifier of the message destination station and the third identifierof the message source station, during an operation 403 (operations 1913,FIG. 19, and 2000, FIG. 20).

In response, the mobile station 1604 returns to the station 1601, bymeans of the base station 1603, a message “MESSAGE_REP<CR, 1601, 1604>,in which the first term represents the content of the response, thesecond the station which is the destination of the response and thethird the station which was the source of the response, during anoperation 404 (operations 2003, FIG. 20, and 1915, FIG. 19).

Next, at the same time, the station 1604 sends a detachment message 406(operation 2106, FIG. 21) to the base station 1603, and the station 1601switches into base station mode (operation 1919, FIG. 19).

Next, the mobile station 1604 synchronises with the base station 1601during an operation 407 (operations 2109 to 2111 and 2113, FIG. 21).Finally, the mobile station 1604 sends a signal of attachment to thebase station 1601, during an operation 408 (operation 2112, FIG. 21).

Next, during an operation which is not shown, the mobile station 1604communicates at a distance, over the external network, by means of thebase station 1601.

According to a variant, when the destination station is a station whichis functioning in base station mode, the synchronisation operationincludes an operation of switching the destination station into mobilemode and an operation of attachment with the source station 1601.

FIG. 23 depicts the electronic circuit of a wireless communicationdevice, using the DECT European standard (specified by the ETSI, ETS 300175, 1991), which can be connected to a network of the STN (SwitchedTelecommunication Network), Ethernet etc type.

This device can be either a DECT base station, or a DECT hybrid station.A DECT base station is responsible notably for providing thesynchronisation of the system. A hybrid station is a communicationstation which can alternately operate as a base station or as a mobilestation. This communication device can be integrated into equipment ofthe computer, printer, fax etc type or be connected to one of the abovementioned items of equipment. The electronic circuit 2300 includes,connected together by an address and data bus 2302:

a radio unit 2301, provided with an antenna 2303,

an input/output controller 2307,

a network controller 2308,

a central processing unit 2306,

a read only memory ROM 2305, and

a random access memory RAM 2304.

In addition, an electrical power supply 2309 is provided for poweringall the components of the electronic circuit 2300 (the electricalconnections concerning the power supply 2309 are not shown).

The network controller 2308 manages the interface with an externalnetwork 2310, for example of the switched telephone network type.

The input/output controller is connected to an information source (forexample an image, sound, text or graphics sensor, a telephone, afacsimile machine, a photographic apparatus, a video camera, a camcorderetc) and/or to an information destination (for example a televisionreceiver, a monitor, a music system, a telephone, a facsimile machine, avideo recorder etc).

All the components illustrated in FIG. 23 are well known to personsskilled in the art of communication circuits with a processor and moregenerally information processing circuits. They are therefore notdetailed here. The electronic circuit 2300 and in particular the centralunit 2306 are adapted to exploit all the capabilities of the DECTstandard known up to the time of the present invention.

The central unit 2306 is also adapted to implement the method of theinvention and, in particular, the flow diagram illustrated in FIG. 32.

The random access memory 2304 stores, in registers which, forconvenience, each bear the same name as the data which they contain:

“Location_Table”: a table containing the data concerning the location ofthe stations in the system;

“CM”: message field; and

“CR”: response field.

The read only memory 2305 stores, in registers which, for convenience,each bear the same name as the data which they contain:

“program1” in which there is stored the operating program of the centralunit 2306.

The read only memory 2305 constitutes a means of storing informationwhich can be read by a computer or a microprocessor, storinginstructions of a computer program characterized in that it makes itpossible to implement the method of the invention. According to avariant, the read only memory 2305 is removable, partially or totally,and has, for example, a magnetic tape, a flash memory, a diskette or afixed-memory compact disc (CD-ROM).

FIG. 24 depicts the electronic circuit of a wireless communicationdevice, using the DECT European standard (specified by the ETSI, ETS 300175, 1991), functioning in mobile station mode.

This device can be either a DECT mobile station, or a DECT hybridstation. This communication device can be integrated into an item ofequipment of the computer, printer, facsimile machine etc type orconnected to one of the aforesaid items of equipment. The electroniccircuit 2400 includes, connected together by an address and data bus2402:

a radio unit 2401, provided with an antenna 2403,

an input/output controller 2407,

a central processing unit 2406,

a screen 2410,

a keyboard 2411,

a read only memory ROM 2405, and

a random access memory RAM 2404.

In addition, an electrical power supply 2409 is provided for supplyingall the components of the electronic circuit 2400 (the electricalconnections concerning the power supply 2409 are not shown).

The input/output controller 2407 is connected to an information source(for example an image, sound, text or graphics sensor, a telephone, afacsimile machine, a photographic apparatus, a video camera, a camcorderetc) and/or to an information destination (for example a televisionreceiver, a monitor, a music system, a telephone, a facsimile machine, avideo recorder etc).

All the components illustrated in FIG. 24 are well known to personsskilled in the art of communication circuits with a processor and moregenerally information processing circuits. They are therefore notdetailed here. The electronic circuit 2400 and in particular the centralunit 2406 are adapted to exploit all the capabilities of the DECTstandard known up to the time of the present invention.

The central unit 2406 is also adapted to implement the method of theinvention and, in particular, the flow diagrams illustrated in FIGS. 29,30 and 31.

The random access memory 2404 stores, in registers which, forconvenience, each bear the same name as the data which they contain:

“relay_response”: a variable containing a message of the type“relay_message_response”

“FP_RELAY”: a variable containing the identity of the base station, withwhich a relay mobile station must synchronise in order to transmit amessage of the “relay-message” type;

“CM”: message field;

“CR”: response field; and

“Location_table”: a table containing the data representing the locationof the stations in the system.

The read only memory 2405 stores, in registers which, for convenience,each bear the same name as the data which they contain:

“program2” in which there is stored the operating program of the centralunit 2406,

“T10”: the maximum value of the waiting time between the sending of amessage “relay_message” and the reception of the response either of the“relay_message_response” type or “report_new_location”, for example 1second.

“T11”: maximum value of the time for seeking synchronisation to a newbase station, for example 500 milliseconds, and

“T12”: the maximum value of the time for seeking synchronisation to theinitial base station, for example 500 milliseconds.

The read only memory 2405 constitutes a means of storing informationwhich can be read by a computer or a microprocessor, storinginstructions of a computer program characterized in that it makes itpossible to implement the method of the invention. According to avariant, the read only memory 2405 is removable, partially or totally,and includes, for example, a magnetic tape, a flash memory, a disketteor a fixed-memory compact disc (CD-ROM).

FIG. 25 depicts a local wireless communication network 2510 comprising:

a first cell 2520 including:

-   -   a DECT base station 2500, connected to an STN network 2511, and    -   a mobile station 2501; and

a second cell 2521 including:

-   -   a base station 2502,    -   a mobile station 2503,    -   a hybrid station 2504 functioning initially in mobile station        mode, and    -   a mobile station 2505.

On initialisation of this system, the mobile station 2501 issynchronised with the base station 2500 and the mobile stations 2503,2504 and 2505 are synchronised with the base station 2502.

In one embodiment of the present invention, if the mobile stations 2504and 2505 wish to communicate together, the base station 2502 initiates asuitable procedure so that the stations 2504 and 2505 communicatedirectly, without transmitting data through the base station 2502. Tothis end, the base station 2502 sends a message to the hybrid station2504, requesting it to switch into base station mode, and a message tothe mobile station 2505 requesting it to synchronise on the station2504.

By virtue of this procedure, two new radio cells 2622 and 2623 arecreated (FIG. 26), which makes it possible to increase the radiopassband available in the local wireless network.

The location table of the base station 2500, in the configurationillustrated in FIG. 25, contains the following information:

Identifier Operating mode Last attachment station 2500 Base 2500 2501Mobile 2500 2502 Base 2500 2503 Mobile 2502 2504 Mobile 2502 2505 Mobile2502

The location table of the base station 2502, in the configurationillustrated in FIG. 25, contains the following information:

Identifier Operating mode Last attachment station 2500 Base unknown 2501Mobile unknown 2502 Base 2500 2503 Mobile 2502 2504 Mobile 2502 2505Mobile 2502

The location table of the base station 2500, in the configurationillustrated in FIG. 26, contains the following information:

Identifier Operating mode Last attachment station 2500 Base 2500 2501Mobile 2500 2502 Base 2500 2503 Mobile 2502 2504 Mobile 2502 2505 Mobile2502

The location table of the base station 2502, in the configurationillustrated in FIG. 26, contains the following information:

Identifier Operating mode Last attachment station 2500 Base unknown 2501Mobile unknown 2502 Base 2500 2503 Mobile 2502 2504 Base 2502 2505Mobile 2504

The location table of the base station 2504, in the configurationillustrated in FIG. 26, contains the following information:

Identifier Operating mode Last attachment station 2500 Base unknown 2501Mobile unknown 2502 Base unknown 2503 Mobile unknown 2504 Base 2502 2505Mobile 2504

It can be seen that, in the configuration illustrated in FIG. 26, thelocation table of the base station 2500 is incorrect with regard to thestations 2504 and 2505.

Under these circumstances, if the base station 2500 wishes to send amessage to a mobile station 2505, it should send it to the cellconsisting of the stations 2504 and 2505 and not, as indicated in itslocation table, to the cell containing the base station 2502.

This error may be the source of delay in transmission and, when theresponse times are fixed by timers, may result in failures to connect.In particular, when a communication is to be established between the STNswitched network 2511 and one of the stations 2504 or 2505, theinformation for the latter station may reach it too late for thecommunication to be able to be established.

The present invention sets out to remedy these drawbacks.

In order to illustrate various embodiments of the present invention, twocases are set out with regard to FIGS. 27 and 28:

FIG. 27 depicts the case where the base station 2500 receives a messagefor the station 2505, in the configuration illustrated in FIG. 26, and

FIG. 28 depicts the case where the base station 2500 receives a messagefor the station 2502, in the configuration illustrated in FIG. 26.

In FIG. 27, there can be seen, on five vertical lines, events, thesending or receiving of messages internal to the DECT network, whichoccur at the stations 2501, 2500, 2502, 2504 and 2505 (in order fromleft to right). The chronological order is complied with in the downwardvertical direction, the first events thus being shown at the top in FIG.27.

First of all, the base station 2500 sends to the mobile station 2501 amessage “relay_request” 2700, which represents a request for thetransmission, by the station 2501, of a message intended for the station2505, in the cell where the station 2505 is situated, according to thelocation table stored by the base station 2500.

In the example described, the message “relay_request” representsinformation according to which a communication coming from the STNnetwork 2511 is intended for the mobile station 2505.

In accordance with the location table stored by the base station 2500,the cell in question is the one where the base station is the station2502.

In response to the message 2700, the mobile station 2501 sends, to thebase station 2500, a message “accept_relay” 2701 accepting or refusingtransmission of a message to the station 2505. Here this message 2701 isan acceptance message.

Then the mobile station 2501 sends, to the base station 2500, adetachment message “detach” 2702 to indicate to the base station 2500that the mobile station 2501 is desynchronising from the base station2500 and that it is therefore no longer able to communicate with thebase station 2500 nor with the mobile stations which are synchronisedwith the base station 2500.

Next, the station 2501 performs an operation 2703 of seeking the basestation 2502, that is to say seeking a synchronisation signaltransmitted by the base station 2502.

Then, as soon as this synchronisation signal has been found, the mobilestation 2501 sends, to the base station 2502, an attachment signal 2704“attach” in order to indicate to it that it is synchronising with thebase station 2502 and that it is able to communicate with the basestation 2502 and/or with any mobile stations which are also synchronisedwith the base station 2502.

Next, the mobile station 2501 sends, to the mobile station 2505, asignal 2705 “relay_message” in order to transmit to it the messagetransmitted to it by the base station 2500.

The base station 2502, which is to transmit this message to the mobilestation 2505, compares the identifier of the destination of thismessage, here 2505, with its location table and determines that themobile station 2505 is not synchronised with the base station 2502.

The base station 2502 then transmits, to the mobile station 2501, amessage 2706 “report_new_location{2505, 2504}” in which the firstidentifier, here 2505, represents the mobile station sought and thesecond identifier, here 2504, represents the base station with which themobile station sought is synchronised.

The mobile station 2501 then transmits, to the station 2502, adetachment message “detach” 2707 in order to indicate to the basestation 2502 that the mobile station 2501 is desynchronising from thebase station 2502 and that it is therefore no longer able to communicatewith the base station 2502 nor with the mobile stations which aresynchronised with the base station 2502.

Next, the station 2501 performs an operation 2708 of seeking the basestation 2504, that is to say seeking a synchronisation signaltransmitted by the base station 2504.

Then, as soon as this synchronisation signal has been found, the mobilestation 2501 sends, to the base station 2504, an attachment signal 2709“attach” in order to indicate to it that it is synchronising with thebase station 2504 and that it is able to communicate with the basestation 2504 and/or with any mobile stations which are also synchronisedwith the base station 2504.

Next, the mobile station 2501 sends, to the mobile station 2505, asignal 2710 “relay_message” in order to transmit to it the messagetransmitted to it by the base station 2500.

In response, the mobile station 2505 transmits, to the mobile station2501, a signal 2711 “relay_message_response” which responds to themessage 2710. In the case depicted, this message 2711 represents anacceptance of establishment of communication with the STN network 2511,by means of the base station 2500.

Next, each of the mobile stations 2501 and 2505 sends a detachmentmessage “detach”, 2712 and 2713 respectively, to the base station 2504.

Then the mobile stations 2501 and 2505 perform operations 2714 and 2715,respectively, of seeking the base station 2500, that is to say seeking asynchronisation signal transmitted by the base station 2500.

Finally, each of the mobile stations 2501 and 2505 transmits anattachment message “attach”, 2716 and 2717 respectively, to the basestation 2500.

The mobile station 2505 next enters into communication with the STNnetwork 2511, by means of the base station 2500.

FIG. 28 depicts the events which follow on from the transmission, by thebase station 2500, to the base station 2502, of a message informing thebase station 2502 that a communication coming from the STN network 2511is intended for the base station 2502.

It can be seen, with the same representation conventions as with FIG.27, that the base station 2502 decides to get into communication withthe STN network 2511, operation 2801. Then the base station 2502 sends,to the mobile station 2503, a message 2802 “report_new_location{2502,2500}” in which the first identifier, here 2502, represents the stationwhich is sending the message and the second identifier 2500 representsthe base station with which the base station 2502 will synchronise.

On reception of this message 2802, the mobile station 2503 performs anoperation 2803 of seeking the base station 2500, that is to say seekinga synchronisation signal sent by the base station 2500.

The base station 2502 then switches into mobile station operating mode,during an operation 2804, and the mobile station 2503 sends, to the basestation 2500, an attachment signal “attach” 2805.

By reading the location table which it stores, the mobile station 2502determines whether the stations which are represented therein have thefollowing two characteristics:

they are operating in base station mode, and

the previous base station to which they were attached is the station2502.

For each of the stations which meet these two characteristics (here onlythe base station 2504 is situated in this case), the mobile station 2502performs an operation 2806 of seeking the base station 2504, that is tosay seeking a synchronisation signal transmitted by the base station2504.

The mobile station 2502 sends, to the base station 2504, an attachmentsignal “attach”, not shown, then a message 2807“report_new_location{2502,2500}” in which the first identifierrepresents the station which is sending the message and the secondidentifier represents the base station with which the station inquestion (the station 2502) will synchronise.

The base station 2504 then performs an operation 2808 of updating itslocation table, replacing this information, for all the stations whichhave the station 2502 as the last base station with which they weresynchronised, with the base station to which the station in question(here the station 2502) will synchronise (here the base station 2500).

Then the mobile station 2502 performs an operation 2809 of seeking thebase station 2500, that is to say seeking a synchronisation signaltransmitted by the base station 2500.

The mobile station 2502 sends, to the base station 2500, an attachmentsignal “attach” 2810.

Finally, the mobile station 2502 sends, to the base station 2500, amessage 2811 “report_new_location{2505,2504}” in which:

the second identifier represents each base station which, in thelocation table stored in the station 2502, has the station 2502 as thelast attachment base station (here only station 2504 is concerned), and

the first identifier represents each mobile station which is attached tothe station identified by the second identifier (here only the station2505 is concerned).

In this way, if there were three base stations concerned and for each ofthem there were five mobile stations concerned, the number of messages“report_new_location” would be fifteen.

Finally, during an operation which is not shown, the base station 2500updates its location table, taking into account the attachmentsrepresented by the messages “report_new_location” and taking the station2500 as the last base station, for the mobile stations which previouslyhad the station 2502 as the last base station.

By virtue of these provisions, the base station 2500 stores a locationtable which takes into account all the former second subcells of thefirst subcell whose base station was the station 2502. Each of thesecond subcells becomes a first subcell of the principal cell whosestation 2500 is the base station.

FIG. 29 depicts an algorithm executed by a relay mobile station whichsends a relay message to a communication station which is notsynchronised with the source of the said message.

In FIG. 29, it can be seen that, first of all, the value of the variable“FP_RELAY” which represents the base station which will serve as arelay, is initialised to the value 2502, during an operation 2900, bythe central unit of the station 2501. Then, during an operation 2901,the station 2501 sends, to the station identified by the value of thevariable “FP_RELAY”, a message “relay_message<CM, 2500>” in which thefirst term “CM”, represents the content of the message intended for themobile station 2505 and the second term 2500, represents the basestation which is the source of the original message (see operation 2705,FIG. 27).

Next, during an operation 2902, the central unit of the station 2501initialises a timer to a value corresponding to a period T10. Then,during a test 2903, the central unit of the station 2501 determineswhether or not a message “relay_message_response” has been received.When the result of test 2903 is positive, during an operation 2904, amessage “relay_response” of the type “relay_message_response<CR, 2500,FP_RELAY>”, in which the first term “CR” indicates the content of theresponse, the second term, 2500, represents the station which is thedestination of the message “relay_response” and the third term,“FP_RELAY”, represents the source station of the message“relay_message_response”, is determined. Then an operation 3116,described below, with regard to FIG. 31, is performed.

When the result of test 2903 is negative, during a test 2905, thecentral unit of the station 2501 determines whether or not a message ofthe type “report_new_location<2505, 2504>” in which the first term,2505, represents the message destination station and the second term,2504, represents the base station with which the destination station issynchronised, has been received.

When the result of test 2905 is positive, an operation 3008 describedbelow with regard to FIG. 30 is performed. When the result of test 2905is negative, during a test 2906, the central unit of the station 2501determines whether or not the timer has a nil value. When the result oftest 2906 is negative, test 2903 is reiterated. When the result of test2906 is positive, during an operation 2907, a message “relay_response”of the type “<NONE, 2500, FP_RELAY>” in which the first term, “None”,contains the response to the previous message (here there is noresponse), the second term, 2500, represents the message destinationstation and the third term, FP_RELAY, represents the station from whicha message “relay_message_response” was awaited. Then the operation 3116described below with regard to FIG. 31 is performed.

In FIG. 30, it can be seen that, following the operation 2905, during anoperation 3008, a detachment message “detach” is transmitted by thestation 2501 to the station 2502. Then, during an operation 3009, atimer corresponding to a period T11 is initialised. Next, during anoperation 3010, the station 2501 searches for a synchronisation signalcoming from the base station 2504. During a test 3011, the central unitof the station 2501 determines whether or not this station has succeededin attaching to the base station 2504. When the result of test 3011 isnegative, during a test 3014, the central unit of the station 2501determines whether or not the timer has a nil value.

When the result of test 3014 is negative, the operation 3010 isreiterated. When the result of test 3014 is positive, the station 2501sends, to the station 2502, an attachment message “attach”, during anoperation 3015, before reiterating operation 2907 (FIG. 29).

When the result of test 3011 is positive, during an operation 3012, thestation 2501 sends, to the station 2504, an attachment message “attach”.

Then, during an operation 3013, the central unit of the station 2501gives the value 2504 to the variable “FP_RELAY” before reiteratingoperation 2901 (FIG. 29).

Following one of the operations 2904 or 2907 (FIG. 29), during anoperation 3116 (FIG. 31), the mobile station 2501 sends a detachmentmessage “detach”. Then, during an operation 3117, the central unit ofthe station 2501 initialises the value of a timer to the valuecorresponding to a period T12.

Next, during an operation 3118, the station 2501 searches for asynchronisation signal sent by the base station 2500. Then, during atest 3119, the central unit of the station 2501 determines whether ornot the station 2501 has succeeded in attaching to the station 2500.When the result of test 3119 is negative, during a test 3122, thecentral unit of the station 2501 determines whether or not the value ofthe timer is nil. When the result of test 3122 is negative, operation3118 is reiterated. When the result of test 3122 is positive, during anoperation 3123, the station 2501 sends an attachment message “attach” tothe station identified by “FP_RELAY”.

When the result of test 3119 is positive, during an operation 3120, thestation 2501 sends, to the station 2500, an attachment message “attach”.Then, during an operation 3121, the station 2501 sends, to the station2500, a message “relay_response”.

FIG. 32 depicts the algorithm executed by the base station which hasreceived an information message on a station serving as a relay (seealso the operations performed by the station 2502, in FIG. 27).

It can be seen, first of all, that, during a test 3201, the central unitof the base station 2502 determines whether or not a message“relay_message <CM,2500>” (in which the first term, CM, represents thecontent of the message and the second term, 2500, represents the stationwhich is the source of the message) intended for the station 2505, hasbeen received. When the result of test 3201 is positive, during a test3202, the central unit of the station 2502 determines whether or not thecommunication station identifier “2505” is present in the location tablestored in the random access memory. When the result of test 3202 isnegative, during an operation 3203, the station 2502 sends, to thestation 2501, a message “relay_message_response<unknown, 2500, 2502>” inwhich the first term, “unknown”, indicates that the station which is thedestination of the message CR to be relayed is unknown, the second term,2500, represents the station which is the destination of the message“relay_response”, and the third term, 2502, represents the sourcestation of the message “relay_message_response”. When the result of test3202 is positive, during a test 3204, the central unit of the station2502 determines whether or not the station 2505 is situated in the samecell as the station 2502. When the result of test 3204 is negative, thestation 2502 sends, to the station 2501, a message“report_new_location<2505, 2504>”, during an operation 3206.

When the result of test 3204 is positive, during an operation 3205, thestation 2502 sends a message “relay_message<CM, 2500>” to the station2505.

1. A method of communicating between communication stations adapted tocommunicate with each other when at least one of the communicationstations supplies a synchronisation signal, the station then functioningin base station mode and the stations not supplying a synchronisationsignal but synchronising on a synchronisation signal sent by a stationfunctioning in base station mode then functioning in mobile stationmode, wherein the method includes: a first operation of receiving amessage, during which a mobile station synchronised with a first basestation receives a message coming from the first base station, anoperation of detachment and attachment, during which the mobile stationsynchronises with a second base station, without the two base stationssynchronising with each other, and a second transmission operation,during which the mobile station transmits the message to the second basestation, and wherein the message represents traffic between the mobilestations synchronised on the first base station and the first basestation, and wherein the message destination station is the second basestation, and the second base station performs, on receipt of themessage, an operation of determining the total traffic during which itdetermines whether or not the sum: of the traffic between the mobilestations synchronised on the first base station and the first basestation, on the one hand, and the traffic between the mobile stationssynchronised on the second base station and the second base station, onthe other hand, is less than a predetermined value.
 2. The methodaccording to claim 1, wherein when, during the total trafficdetermination operation, it is determined that the sum: of the trafficbetween the mobile stations synchronised on the first base station andthe first base station, on the one hand, and the traffic between themobile stations synchronised on the second base station and the secondbase station, on the other hand, is less than the predetermined value,one of the base stations performs an operation of switching into mobilestation mode and synchronises on the other base station.
 3. A method ofcommunicating between communication stations adapted to communicate witheach other when at least one of the communication stations supplies asynchronisation signal, the station then functioning in base stationmode and the stations not supplying a synchronisation signal butsynchronising on a synchronisation signal sent by a station functioningin base station mode then functioning in mobile station mode, whereinthe method includes: a first operation of receiving a message, duringwhich a mobile station synchronised with a first base station receives amessage coming from the first base station, an operation of detachmentand attachment, during which the mobile station synchronises with asecond base station, without the two base stations synchronising witheach other, and a second transmission operation, during which the mobilestation transmits the message to the second base station, and whereinthe message represents traffic between the mobile stations synchronisedon the first base station and the first base station, and wherein themessage destination station is the second base station, and on receptionof the message, the second base station performs a first operation ofdetermining the distribution of traffic between the two base stationsduring which the second mobile station determines whether or not: on theone hand, the traffic between the mobile stations synchronised on thefirst base station and the first base station is less than apredetermined value, and on the other hand, the traffic between themobile stations synchronised on the second base station and the secondbase station is greater than a predetermined value.
 4. The methodaccording to claim 3, wherein when, during the first trafficdistribution determination operation, it is determined that: the trafficbetween the mobile stations synchronised on the first base station andthe first base station is less than a predetermined value, on the onehand, and the traffic between the mobile stations synchronised on thesecond base station and the second base station is greater than apredetermined value, on the other hand, the second base station performsan operation of seeking a communication to be transferred during whichthe second mobile station determines whether at least one of thecommunications between mobile stations which are synchronised with thesecond base station can be transferred to the first base station.